1. Technical Field of the Invention
This invention pertains to inventive methods of manufacturing a semiconductor device for improving device performance, and to the resulting unique high-performance device structure. In particular, this invention has improved charge mobility in FET devices by structurally imposing tensile and compression forces in a device substrate during device fabrication.
Within the field of semiconductor device design, it is known that mechanical stresses within the device substrate can modulate device performance. Individual stress tensor components affect device behavior of PFETs and NFETs differently. Previous improvements that utilized stress enhancements tended to focus on one or the other type of device outside of a practical performance environment, such as in an IC chip. In order to maximize the performance of both PFETs and NFETs within IC chips, the stress components need to be engineered and applied differently, yet simultaneously. The best stress design is tension in both directions for the nFET and compression in the longitudinal direction for the pFET along with tension in the transverse direction relative to channel current. In this invention we show a method and structure by which we can use spacers to introduce a longitudinal tensile stress for the nFET while at the same time applying a longitudinal compressive stress on the pFET device in a conventional FET structure, and selectively deposited layers on silicon-on-insulator (“SOI”) structures. The longitudinal stress is induced along the same axis as the current, or charge, being carried in the channel. It may be more difficult to impose a stress in the transverse direction using spacers so we lose benefit from that direction. However, by virtue of the fact that we can move the stress inducing component closer to the device through the use of stress inducing spacers and layers, the modulation of stress can be improved relative to the isolation material or STI stress approach as suggested in the patent application identified above. One advantage of the method and structure of the present invention that it has provided a device performance improvement for both the nFET and pFET simultaneously.
2. Description of the Prior Art
Ito et al (IEDM, 2000) impose stress using an etch-stop nitride superlayer that is deposited after the device is completely constructed. Again, here the films have a built-in intrinsic biaxial stress which they modulated from compressive through tensile. They found that when the film is in tension the nFET performance is enhanced while that of the pFET's is degraded. They found the reverse for compression, namely nFET is degraded while the pFET is enhanced. They could not improve the performance of both the pFET and nFET simultaneously. Also, since the film is well above the device the stress translated down into the silicon will be somewhat lesser, particularly when compared to material that is adjacent to the device.
In the application identified above entitled “Isolation Structures for Imposing Stress Patterns”, we showed how to modulate the stresses imposed on the silicon by isolation (the preferred example used STI). One of the embodiments advocates the use of materials with different intrinsic stress and coefficients of expansion mismatched in the appropriate regions of the nFETs and pFETs to modulate induced stresses. In another embodiment, we discussed how to add compressive stress by oxidation through openings in a nitride liner as needed for pFETs in the longitudinal direction, while retaining all the tensile stresses (in the transverse pFET direction and transverse+longitudinal nFET directions) from intrinsic and thermal mismatch properties. Prior to these two recent disclosures, all prior known solutions and methods using mechanical stress for device performance enhancement improved neither both nFETs and pFETs simultaneously nor taught the individual device isolation structures and methods of making them. In the present specification we leverage stress effects on devices using stress induced by spacers and by processing, e.g. oxidizing, a selectively deposited silicon isolation liner on SOI structures. We also show how to modulate the stresses for both pFETs and nFETs, which brings the stress effect much closer to the device.